Reactance measuring device



Sept. 13, 1949. v R. L. RINGER, JR 1,6 7

REACTANCE MEASURING DEVICE I Filed June 23, 1944 LL INVENTOR.

zwmflw HTTOFIWE? Patented Sept. 13, 1949 REACTANCE MEASURING DEVICE rum-c Lee Ringer, Jr., Jersey City, N. 1., minor to Allen B. Du Mont Laboratories, Inc., Passaio, N. 1., a corporation of Delaware I Application June 23, 1944, Serial No. 541,824

'1 Claim.

This invention relates to a device for measuring inductances or capacitances. It is particularly useful for measuring the inductance of coils or other devices that possess inductive reactance and for measuring capacitances of condensers.

In carrying out the invention-an inductometer or capacitance meter is provided by means of which inductances or capacitances of wide ranges can be ascertained very rapidly and accurately without requiring the skill of highly trained operators. The inductor to be measured, such as a coil, for example, is placed in parallel with a known condenser, or the condenser to be measured is placed in parallel with a known inductance, and alternating current is applied to the parallel combination at resonant frequency. The measurements may be taken even while direct current is flowing through the inductor.

The invention may be understood from the description in connection with the accompanying drawing in which:

Fig. 1 is a diagram of connections; and

Fig. 2 shows a modification of Fig. 1.

In the drawing, reference character I indicates a source of direct current, the voltage of hich is variable but can be kept constant at "y desired potential. Leads 2 and 3 extend um the supply I. A resistor l is connected across .nese leads and an ammeter '5 is located in lead 2. A capacitor 6 of known capacitance is located in the lead 3, and a resistor I is connected in series therewith. The secondary 8 of a transformer 9 is connected across the leads 2 and 3. The primary 10 of this transformer is connected to a source ll of alternating current of constant voltage but variable frequency. This source of current is represented diagrammatically as such devices are well known.

A dial or control for varying the frequency is indicated at. II. It is provided with a pointer l3 and a graduated scale I for indicating the frequencies to which the alternator II is adjusted.

A cathode-ray tube T is indicated somewhat diagrammatically. The ends of resistor I are connected by leads II to amplifier it from which signals are fed by leads I! to a pair ll of the deflection plates of the tube '1. A capacitor I9 is located in one of the leads I.

Inductance is measured as follows: The reactor or inductor of which the inductance is to be measured or determined is connected at :c, Fig. 1, in parallel with the fixed capacitor of known capacitance. The capacitor I and inductor a: constitute a tank circuit in series with the resistors 4 and l, ammeter 5 and the low impedance secondary 8 of transformer 9. The voltage of the D. C. supply I is adjusted so that the 'ammeter 5 indicates the direct current at which the inductance of coil :1: is to be ascertained. The inductance may, however, be ascertained without any direct current. The frequency of the A. 0. generator II which feeds the primary I0 of transformer 9 is adjusted to the frequency at which the tank circuit 62 is at resonance, which is the condition that obtains when the indication on the cathode-ray tube T is a minimum.

As indicated in Fig. 2, the cathode-ray tube 20 may be connected across the capacitor 8 and inductor :t, which are in parallel, instead of being connected across the resistor I. In this case the frequency at which the tank circuit G-a: is at resonance is indicated by the maximum deflection indicated on the cathode-ray tube T.

Since the frequency and the capacitance 6 are known, the inductance a: can be calculated from the formula 2r\ L C' or the formula can be used to measure the inductance of an unknown coil without the necessity of comparing it with a known coil or the capacitance of a capacitor without comparing it with a known capacitor; and its use requires little time and practically no training of the operator.

While the invention has been particularly described for measuring inductance, it will be clear that it is also adapted to the measurement of capacitance in the same way. This can be done by placing a known inductance where the capacitor 8 is and the unknown capacitor where the former coupling said source to a circuit which comprises a reactive impedance of known value in series with a known resistance, said known impedance being in parallel with said reactance that is to be measured, and a reactance'indieating device connected to opposite ends 01, said resistance that is located in said circuit, said nonsm- LEE RmGEB, Ja.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,960,333 Du'Mont May 29, 1934 OTHER REFERENCES Radio Instruments and MeasurementsjU. S.

Bureau of Standards, 1918, pages 136-137.

Radio World, July 1936, pages 45-46.

Wireless World, Feb. 1944, article by Blackwell et al., pages 37-40.

Everitt, Communication Engineering, McGraw- Hill, 1937, pages 78-79.

Radio World, Dec. 1936; pages 12-13. 

